Unhandled Exception: Converting object to an encodable object failed: Instance of '_$RecordStandardNoteModel'

`
Future fetchSavePlayRecord() async {

PlayRecordModel responseRecord = _musicEngine.recordEngine.responseRecord;

ListBuilder temp = responseRecord.playNoteList.toBuilder();

print(temp);
print("==============");
// final Iterable types = new BuiltList([RecordStandardNoteModel]);

ResultData res = await _pianoService.savePlayRecordDetail(
endPlayTime: responseRecord.endPlayTime,
startPlayTime: responseRecord.startPlayTime,
taskType: responseRecord.taskType,
teachingType: responseRecord.teachingType,
standardDuration: responseRecord.standardDuration,
relationId: responseRecord.relationId,
metronomeMark: responseRecord.metronomeMark,
musicId: responseRecord.musicId,
playNoteList: responseRecord.playNoteList.toList(), // i want get a list
);

if (res.code == 0) {
} else {
showToast(res.msg]);
}
}
`